1. Technical Field of the Invention
The present invention relates to an image display device suitable for an information display apparatus or the like.
2. Description of the Related Art
A variety of image display devices include a sprite attribute table, which stores attribute data representing display attributes such as a display position, a magnification ratio, or the like of a sprite to be displayed, and can display an image of the sprite on a display according to the attribute data stored in the sprite attribute table. Such image display devices have been suggested, for example, in Japanese Patent Application Publication No. 2000-35781.
In some image display devices, an animation is displayed on a display by changing the display position of the sprite. FIG. 5 is a block diagram illustrating a configuration of part of a conventional image display device 10 which includes such an animation display function.
In FIG. 5, a display memory 3 is a memory that stores image data to be displayed on a display (not shown). The display memory 3 may be a frame memory that stores image data in units of frames (i.e., in units of screens). The display memory 3 may also be a line memory that stores image data in units of lines (i.e., in units of horizontal scan lines). Sprite attribute tables 1A and 1B are a table that stores attribute data representing display attributes of a sprite as described above. The sprite attribute tables 1A and 1B are alternately selected as a sprite attribute table for drawing and a sprite attribute table for update, respectively. A sprite rendering processor 2 performs a drawing process, which reflects an image of the sprite to a display screen of the display, by reading pattern data of the sprite stored in a pattern memory (not shown) and storing the read pattern data in the display memory 3. Here, with reference to one of the sprite attribute tables 1A and 1B which is selected as a table for drawing, the sprite rendering processor 2 performs, for example, a process for determining the address of the pattern data of the sprite in the display memory 3 to allow the sprite to be displayed at a display position represented by the attribute data.
In the case where an animation is displayed on the image display device 10, a CPU which controls the image display device 10 repeats a process which rewrites (or updates) attribute data in one of the sprite attribute tables 1A and 1B, which is selected as a table for update and switches the sprite attribute table for update to a sprite attribute table for drawing.
FIG. 6 is a time chart illustrating an example of the operation of such animation display. In the example shown in FIG. 6, “VSYNC_N” is a vertical synchronous signal provided to the display, and a period from a falling edge of the vertical synchronous signal VSYNC_N to a next falling edge thereof is one vertical scan period (i.e., one frame) for displaying an image corresponding to one frame. The display memory 3 is a frame memory which can store image data of two frames.
In the example shown in FIG. 6, in frame 1, the sprite attribute table 1A is selected as a table for update and the sprite attribute table 1B is selected as a table for drawing. Thus, the CPU writes attribute data 1 in the sprite attribute table 1A. Then, in frame 2, the sprite attribute table 1A is selected as a table for drawing and the sprite attribute table 1B is selected as a table for update. Thus, the sprite rendering processor 2 performs a drawing process that stores pattern data of the sprite in the display memory 3 according to the attribute data 1 stored in the sprite attribute table 1A for drawing. On the other hand, the CPU writes attribute data 2 to the sprite attribute table 1B for update.
Then, in frame 3, the sprite attribute table 1A is selected as a table for update and the sprite attribute table 1B is selected as a table for drawing. Thus, the sprite rendering processor 2 performs a drawing process that stores pattern data of the sprite in the display memory 3 according to the attribute data 2 stored in the sprite attribute table 1B for drawing. On the other hand, the CPU writes attribute data 3 to the sprite attribute table 1A for update. In parallel with these operations, in frame 3, image data that is stored in the display memory 3 in frame 2, i.e., pattern data of the sprite drawn according to the attribute data 1, is read from the display memory 3 and displayed on the display.
Then, in frame 4, the sprite attribute table 1A is selected as a table for drawing and the sprite attribute table 1B is selected as a table for update. Thus, the sprite rendering processor 2 performs a drawing process that stores pattern data of the sprite in the display memory 3 according to the attribute data 3 stored in the sprite attribute table 1A for drawing. On the other hand, the CPU writes attribute data 4 to the sprite attribute table 1B for update. In parallel with these operations, in frame 4, image data that is stored in the display memory 3 in frame 3, i.e., pattern data of the sprite drawn according to the attribute data 2, is read from the display memory 3 and displayed on the display.
As described above, the attribute data used for drawing of the sprite is switched in the order of attribute data 1→attribute data 2→attribute data 3→attribute data 4. The displayed form of the sprite is changed in this manner to display an animation.
However, the conventional image display device described above has a problem in that CPU load for animation display is increased since the CPU must frequently write attribute data to each sprite attribute table in order to perform animation display.